Automated and semi-automated product dispensing systems are becoming increasingly popular for dispensing products such as fuel for large fleet users or for private owners or for making banking transactions during hours when banks normally are closed. To permit use of these systems, generally a card reader control panel or control station is employed; and the transaction is initiated by insertion of an identified/credit card into a card reader by the customer or user of the system. These cards are uniquely encoded with indicia particularly identifying the customer or user and, in many cases, include other indicia to limit the type and quantity of product which may be purchased or withdrawn from the system in response to the use of the card.
Automated fuel dispensing systems exist which are operated in response to the insertion of uniquely encoded credit documents into a card reader. These systems then permit the withdrawal of particular types and quantities of fuel from fuel pumps controlled by the system and in addition, prepare the necessary billing information concerning the transaction for subsequent billing to the customer or card holder.
At least some of the data on the card in some such systems is then transmitted from the card reader to a remote or local computer for verification; and if the document is verified as an authorized document, the system permits the withdrawal of fuel under the control of the credit card. When a remote computer is used for the credit card verification, it is necessary for a committed transmission link to be employed between the location of the fuel pumps and the central computer location. This results in a relatively expensive system and limits the flexibility which is available at any given fuel dispensing site.
In the fuel dispensing systems of the above co-pending applications, a local control console is used to control a number of different dispensers without the necessity of verification of each transaction or a portion of each transaction by a central computer located remotely from the fuel dispensing site. The particular manner in which a credit card is checked to determine whether it is a valid card or a non-valid card can vary substantially. A most direct manner of verification is to uniquely encode a binary word (or words) on each card which identifies it and then to compare this word in a comparator against that same word stored in a memory where it is further identified as being either "valid" or "non-valid". Such an approach, however, requires a relatively large capacity memory, particularly if there are a large number of different credit cards in use in the system with which the local fuel dispenser is associated. A similar problem exists in conjunction with automatic bank tellers where a verification of the validity of the inserted credit document must be made prior to permitting a transaction to take place.
As a consequence, it is desirable to provide a system for checking the validity of a credit document quickly and easily at the location where the document itself is used and which further requires a minimum memory capacity in order to effect the necessary document check.